Normal forms of quadratic vector fields and the Shi Songling equation
The paper contains a method for the localization of limit cycles for planar vector fields with a weak focus. This method is applied to analyze a large domain on the phase plane for the Shi Songling example -- a quadratic vector field with at least four limit cycles. In a neighborhood of the singular point \(O(0,0)\) three very narrow annuli are obtained in each of which there is a unique limit cycle.
scientific article; zbMATH DE number 5824114